We have a PIWIK Installation with about 25 Sites and about 15.000 visits per month running for about 4 years. Since the update on 3.1.1 PIWIK shows no pageviews for all the pages. The whole “Actions” part is empty. Archiver is running with no errors.
Furhermore we detected, that in the archive_numeric table no new entries with the “Actions_” prefix were created since the update
Please make sure that all plugins (especially the “Actions”-PLugin) was updated correctly and that it’s running. You can see the plugin list in Settings > System > Plugins.